Communication devices such as User Equipments (UE) are enabled to communicate wirelessly in a radio communications system, sometimes also referred to as a radio communications network, a mobile communication system, a wireless communications network, a wireless communication system, a cellular radio system or a cellular system. The communication may be performed e.g. between two user equipments, between a user equipment and a regular telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications network.
User equipment are also known as e.g. mobile terminals, wireless terminals and/or mobile stations, mobile telephones, cellular telephones, or laptops with wireless capability, just to mention some examples. The user equipments in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity.
The wireless communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by a network node such as a Base Station (BS), e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNB, eNodeB, NodeB, B node, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several radio access and communication technologies. The base stations communicate over the radio interface operating on radio frequencies with the user equipments within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: GroupeSpécial Mobile).
In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the user equipment. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the user equipment to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipments. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
According to 3GPP/GERAN, a user equipment has a multi-slot class, which determines the maximum transfer rate in the uplink and downlink direction, GERAN is an abbreviation for GSM EDGE Radio Access Network. EDGE is further an abbreviation for Enhanced Data rates for GSM Evolution.
The past 30 years have seen a tremendous improvement in the state of Information and Communication Technologies (ICT), formally led by the Computing and the Telecommunications industries. This improvement is most felt in the increase in global Internet traffic, which has been conservatively predicted to reach a ten-fold growth from 2010 levels by 2016. Other forecasts by Cisco predict an increase in traffic of as much as a 92% cumulative annual growth rate; this amounts to a 700-fold increase in traffic by 2020.
A majority of this traffic growth is expected to come from the increased consumption of video on mobile networks, as well as a net increase in subscribers transitioning to mobile broadband even as the fixed and mobile networks converge to provide end-user experience that is indistinguishable in many environments. Added to this, it has been predicted that the mobile broadband industry will get most of its growth in the number of connections from the widespread introduction of Machine Type Communication (MTC) devices that will drive the Machine-to-Machine (M2M) market for applications from diverse industries such as Utilities (e.g. Smart Grid), Automotive (e.g. Intelligent Transportation), Health care. Apart from these industries, the broad area of Industrial Automation is expected to create new business opportunities in a variety of industries such as Agriculture, Mining and Exploration, Oil and Natural Gas Distribution, Residential and Building Automation etc. Estimates of the number of devices vary widely from our own declamation of an increase from 5 billion subscriptions to 50 billion connected devices.
One key development that is inevitable is a merging of fixed and wireless networks in what has been termed as the Fixed Mobile Convergence (FMC).
There is still some scope for a part of the predicted traffic increase to happen due to network build out in areas of the world not covered by mobile broadband. However, it is also true that much of the increase in data traffic will happen based on the kind of activities people engage in over the Internet, such as the transition of video services from broadcast networks to online video sources. This leads to our conviction that the bulk of Internet traffic increase will happen in areas that are already served by cellular networks.
Table 1 below is a generational classification of broadband cellular technologies. The table uses an accepted and correct technical classification, while it is acknowledged that industry and media may often use a more sensational approach to distinguishing a generation. With the introduction of LTE and all indications of LTE being the sole surviving cellular standard, it is now possible to identify a true convergence of mobile radio technologies.
TABLE 1generational classification of broadband cellular technologies. The datarates are in orders of magnitude and the numbers are approximations.International Telecommunication Union (ITU) ClassificationInternational MobileTelecommunciations 2000IMT-(IMT-2000)AdvancedGeneration1G2G3G4GTechnologyAMPS/NMTGSM/EDGEWCDMA/HSPA3GPP LTEExamples(as component ofCDMA2000/evDOIEEE 802.16-2009EIA/TIA-136)WiMAX rel. 1.1EIA/TIA-95TypeAnalogDigitalDigitalDigitalChannelization<100KHz<1MHz<10MHz<100MHzFrequency band400-1000MHz400-2000MHz400-3000MHz200-5000MHzData rates<10kb/s/user<1Mb/s/cell<100Mb/s/cell<1Gb/s/cellServicesVoice telephonyVoice/dataVoice/DataData (voiceincluded)
The US National Broadband Plan aims to create new allocations for mobile, fixed and unlicensed broadband access of up to 500 MHz of spectrum below 5 GHz by 2020 (FCC, “Connecting America: The National Broadband Plan,” at http://www.broadband.gov, March 2010.) Currently 547 MHz has been designated as flexible use spectrum for wireless broadband, of which roughly 170 MHz is available to cellular and Personal Communications Service (PCS) operators. With the existing allocations of 547 MHz of spectrum including the recent Advanced Wireless Services-1 (AWS-1) auctions, this should give the mobile industry over 800 MHz of spectrum to improve their ability to handle more users and newer services. Even with such largesse, it is inconceivable that system capacity for cellular networks will improve by an order of magnitude in the future without significant reengineering of the way networks are deployed.
It should be noted that the lack of spectrum has driven wireless network deployment in two directions.
Firstly, every system has improved throughputs as well as spectral efficiency over the previous generation using a variety of technological approaches such as                a reduction in cell size through densification of the network, the development of Heterogeneous networks (hetnets) as a means of boosting capacity and bitrates,        deployment of additional spectrum,        packet data based on the Internet Protocol (IP),        wider bandwidths,        link adaptation using adaptive modulation and coding, and Hybrid-Automatic Repeat reQuest (HARQ),        higher order modulation schemes,        antenna techniques such as beamforming and Multi-Input Multi-Output (MHO),        advanced receiver architectures such as Successive Interference Cancellation (SIC), multi-stage SIC, joint demodulation,        advanced network procedures such as interference coordination.        
These techniques have provided the means to increase peak spectral efficiencies per link to as much as 15 b/s/Hz. Of course, the observed cell spectral efficiencies vary according to the radio environment and the interference level and typically are of the order of 1-3 b/s/Hz on average.
Secondly, systems such as LTE that may operate over channel bandwidths of up to 100 MHz do so with the aid of carrier aggregation. Aggregation of carriers cannot be done arbitrarily and radio requirements become very complicated when specifying the particular combinations of carrier bandwidths that may be used to populate a band or combined across bands.
Given the state of spectrum allocations for mobile systems, it is of interest to see if the evolution of modern mobile networks may proceed beyond 4G. The objective of such an evolution would be to improve data rates by yet another order of magnitude over the last generation, and to moreover do this under the assumption of a dense deployment of infrastructure nodes providing radio links to mobile users. Such a network would also need to do be deployed with much larger spectrum allocations, typically operating under conditions of low to moderate mobility. The reach of such a network would span indoor locations as well as densely populated urban centers.
Today's cellular communication occurs largely in frequency bands below 3 GHz in what we term as an interference-limited environment. While LTE may operate over bandwidths of as much as 100 MHz by design, the future radio access system we envisage would operate over bandwidths of the order of 1 GHz. Clearly, such a system could not operate in bands below 3 GHz. The lowest band where the mobile industry may home for spectrum parcels that exceed the 10-40 MHz of contiguous allocations typical for the industry is probably above 3 GHz. Of the regions of spectrum that are most promising for the mobile industry, the cm-Wave (CMW) region from 3-30 GHz and the mm-Wave (MMW) region from 30-300 GHz may be considered as being particularly interesting for the next generation mobile systems.
Table 2 is a link budget for a pair of radios that are configured to operate in two modes. By the term “radios” when used herein is meant devices comprising both transmission and reception functions. The first mode is a low data rate mode using low antenna gain and the second mode is a high data rate mode using high antenna gain. It is well known that such a variation in antenna gain may be obtained by using active antenna solutions composed of many antennas integrated with a set of radio chains that are at most equal in number to the number of antenna elements. The conducted power from the transmitters are transferred to the antenna elements through a transfer matrix that may adjust the phase and optionally the amplitude of the transmitter outputs so as to create a resultant directivity pattern for the antenna array that may either have a high gain or a low one. Typically, the tradeoff in such an arrangement is between the spatial region covered by the antenna, which is large for a low effective array gain, and is narrow when a high gain is chosen.
TABLE 2Link budget at 40 GHz for a pair of radios that is able totrade off data rate for antenna gain. A free space propagationloss model has been used for illustrative purposes. Shadowinglosses are meant to represent all possible additional propagationlosses. Some common losses such as those at the transmit andreceive switch may have been ignored.ParameterCase 1 link budgetCase 2 Link budgetTx Power: P_TX20dBm20dBmTx Antenna Gain: G_T2dB14dBEquivalent Isotropically22dBm34dBmRadiated Power (EIRP)Bandwidth1GHz1GHzNoise power: kTB−84dBm−84dBmRx Antenna Gain: G_R0dB14dBReceiver Noise Figure (NF)7dB7dBReceiver Sensitivity Margin2dB2dBShadowing margin3dB3dBCarrier-to-Noise Ratio (C/N)−3dB14dBneeded(0.1 b/s/Hz)(5 b/s/Hz)Required received power−72dBm−61dBmPath loss budget94dBm95dBmRange (40 GHz)30m30m
In a system that transmitter wise relies on narrow beams to obtain the required link budget a problem is to enable a receiving device to find the transmitting system, i.e. to make the receiving device aware of the presence of the system.
In traditional cellular systems such a signal is typically transmitted with a very wide beam pattern thus enabling receiving devices in the coverage area of the wide beam to detect the system.
In a system that relies on high-gain transmitter beamforming to achieve the required link budget a wide beam may not convey sufficient energy into a given direction for a receiving device to detect the system. In IEEE 802.11ad standard this problem is solved by beamforming a wideband discovery signal into one particular direction and in a Time Division Multiplexing (TDM) fashion cycle through different transmit directions to cover the complete area of interest.
A problem is that this solution cannot be applied to an envisioned Super-Densed Network (SDN) wherein also narrowband devices should be capable of accessing the system since they cannot receive a wideband discovery signal.